mjmlio/mjml · warning

"dependencies" must be an object.

Error message

"dependencies" must be an object.

What it means

assignDependencies expects its first argument to be a plain object mapping tags to arrays. When the dependencies argument is not an object (null, array misuse, string, undefined), it warns '"dependencies" must be an object.' and returns an empty/unchanged target, so no dependencies get registered.

Source

Thrown at packages/mjml-validator/src/dependencies.js:23

  for (const source of sources) {
    if (typeof source === 'object' && source !== null) {
      for (const tag of Object.keys(source)) {
        if (typeof tag === 'string') {
          const list = []
          if (target[tag]) {
            list.push(...target[tag])
          }
          if (source[tag]) {
            list.push(...source[tag])
          }
          target[tag] = Array.from(new Set(list))
        } else {
          console.warn('dependency "tag" must be of type string')
        }
      }
    } else {
      console.warn('"dependencies" must be an object.')
    }
  }
  return target
}

const dependencies = {}

export const registerDependencies = (dep) => {
  assignDependencies(dependencies, dep)
}

export default dependencies

View on GitHub (pinned to 6c01d35af5)

Solutions

1. Pass a well-formed object: registerDependencies({ 'mj-accordion': ['mj-accordion-element'] })
2. Validate the argument before calling: if (deps && typeof deps === 'object' && !Array.isArray(deps))
3. Fix the upstream config loading that produced null/undefined
4. Add a fallback default ({} ) at the call site

Example fix

// before
registerDependencies(config.dependencies) // undefined
// after
const deps = config.dependencies && typeof config.dependencies === 'object' ? config.dependencies : {}
registerDependencies(deps)

if (deps == null || typeof deps !== 'object' || Array.isArray(deps)) {
  throw new Error('dependencies must be an object of tag -> array')
}

const isDependenciesObject = (d) => d != null && typeof d === 'object' && !Array.isArray(d)

When it happens

Trigger: Calling registerDependencies(null), registerDependencies('mj-button'), or passing a non-object from a misparsed config into registerDependencies/assignDependencies.

Common situations: Config file failed to parse and yielded null; a caller passed a list instead of a map; optional import resolved to undefined; refactors renaming the config field.

Related errors

• dependency "tag" must be of type string
• "dependencies" option should be provided to mjml validator
• An mj-head element add an unkown head attribute : ${attr} wi
• ValidationError: \n ${errors.map((e) => e.formattedMessage).
• Malformed MJML. Check that your structure is correct and enc

AI-assisted analysis of mjmlio/mjml@6c01d35af5 (2026-09-02). Data as JSON: /api/errors/667ab7035cad5562. Report an issue: GitHub.